Revealing abnormal micro- and meso-structure evolution mechanism of porous pyrolytic carbon in TRISO coated fuel particles under high-temperature treatment

However, its unique low-density and porous structure leads to uncertainty in the high-temperature structural evolution behavior. In this study, PPyC was subjected to heat treatment from 1200°C to 1600°C. Results clearly identify 1400°C as the key structure-performance evolution threshold.

Below this temperature, structural evolution is dominated by oxygen-defect migration. Above it, transition zones between amorphous and crystalline domains generate abundant vacancies, while grain-boundary pinning restricts atomic motion and increases structural disorder. The combined effects of sintering-neck formation, interlayer shrinkage, and theoretical particle-volume expansion drive the dynamic evolution of the pore structure, leading to a reversible open-to-closed pore transition at the mesoscale.